Buggy code:
public class URLRewritingModifier extends AbstractTestElement implements Serializable , PreProcessor { private static final long serialVersionUID = 233L ; private static final String SEMI_COLON = ";" ; private transient Pattern pathExtensionEqualsQuestionmarkRegexp ; private transient Pattern pathExtensionEqualsNoQuestionmarkRegexp ; private transient Pattern parameterRegexp ; private transient Pattern pathExtensionNoEqualsQuestionmarkRegexp ; private transient Pattern pathExtensionNoEqualsNoQuestionmarkRegexp ; private static final String ARGUMENT_NAME = "argument_name" ; private static final String PATH_EXTENSION = "path_extension" ; private static final String PATH_EXTENSION_NO_EQUALS = "path_extension_no_equals" ; private static final String PATH_EXTENSION_NO_QUESTIONMARK = "path_extension_no_questionmark" ; private static final String SHOULD_CACHE = "cache_value" ; private transient String savedValue = "" ; public void process ( ) { JMeterContext ctx = getThreadContext ( ) ; Sampler sampler = ctx . getCurrentSampler ( ) ; if ( ! ( sampler instanceof HTTPSamplerBase ) ) { return ; } SampleResult responseText = ctx . getPreviousResult ( ) ; if ( responseText == null ) { return ; } initRegex ( getArgumentName ( ) ) ; <START_BUG> String text = new String ( responseText . getResponseData ( ) ) ; <END_BUG> Perl5Matcher matcher = JMeterUtils . getMatcher ( ) ; String value = "" ; if ( ( ( isPathExtension ( ) ) && ( isPathExtensionNoEquals ( ) ) ) && ( isPathExtensionNoQuestionmark ( ) ) ) { if ( matcher . contains ( text , pathExtensionNoEqualsNoQuestionmarkRegexp ) ) { MatchResult result = matcher . getMatch ( ) ; value = result . group ( 1 ) ; } } else if ( ( isPathExtension ( ) ) && ( isPathExtensionNoEquals ( ) ) ) { if ( matcher . contains ( text , pathExtensionNoEqualsQuestionmarkRegexp ) ) { MatchResult result = matcher . getMatch ( ) ; value = result . group ( 1 ) ; } } else if ( ( isPathExtension ( ) ) && ( isPathExtensionNoQuestionmark ( ) ) ) { if ( matcher . contains ( text , pathExtensionEqualsNoQuestionmarkRegexp ) ) { MatchResult result = matcher . getMatch ( ) ; value = result . group ( 1 ) ; } } else if ( isPathExtension ( ) ) { if ( matcher . contains ( text , pathExtensionEqualsQuestionmarkRegexp ) ) { MatchResult result = matcher . getMatch ( ) ; value = result . group ( 1 ) ; } } else { if ( matcher . contains ( text , parameterRegexp ) ) { MatchResult result = matcher . getMatch ( ) ; for ( int i = 1 ; i < ( result . groups ( ) ) ; i ++ ) { value = result . group ( i ) ; if ( value != null ) { break ; } } } } if ( shouldCache ( ) ) { if ( ( value == null ) || ( ( value . length ( ) ) == 0 ) ) { value = savedValue ; } else { savedValue = value ; } } modify ( ( ( HTTPSamplerBase ) ( sampler ) ) , value ) ; } private void modify ( HTTPSamplerBase sampler , String value ) { } public void setArgumentName ( String argName ) { } private void initRegex ( String argName ) { } public String getArgumentName ( ) { } public void setPathExtension ( boolean pathExt ) { } public void setPathExtensionNoEquals ( boolean pathExtNoEquals ) { } public void setPathExtensionNoQuestionmark ( boolean pathExtNoQuestionmark ) { } public void setShouldCache ( boolean b ) { } public boolean isPathExtension ( ) { } public boolean isPathExtensionNoEquals ( ) { } public boolean isPathExtensionNoQuestionmark ( ) { } public boolean shouldCache ( ) { } }

Fix:
String text = responseText . getResponseDataAsString ( ) ;